1. Field of the Invention
The present invention relates to a technique of making adjustments for a hearing aid. More specifically, the present invention relates to a technique of utilizing an electroencephalogram of a user who is wearing a hearing aid to identify phonemes which are difficult for the user to hear, and adjusting a correction process in the hearing aid to realize better hearing.
2. Description of the Related Art
In recent years, due to the aging society, increased opportunities for listening to loud music for long hours, and other influences, there is an increasing number of people suffering from presbycusis or hypacusia associated with acoustic traumas. Moreover, due to the downsizing and improved performance of hearing aids, users feel less of a psychological barrier against wearing hearing aids, and there is an increasing number of users who use hearing aids to be able to hear daily conversations more clearly.
A hearing aid is a device for compensating for the deteriorated hearing of a user through sound amplification. The amount of sound amplification which a user desires in a hearing aid depends on the level of deterioration in the hearing of the user, and on the frequency band. Therefore, before beginning use of a hearing aid, “fitting” is required for adjusting the amount of sound amplification for each frequency, in accordance with the hearing of each user.
Fitting is generally performed based on each user's audiogram. An “audiogram” is a result of evaluating how a pure tone of each frequency is heard; for example, a diagram in which, for each of a number of sounds of different frequencies, the smallest sound pressure level (decibel value) that the user can hear is plotted against frequency. An audiogram is created at a hearing aid shop or a medical institution.
A hearing aid shop or a medical institution first generates an audiogram for each user. Then, from the audiogram, an amount of amplification is determined and an initial adjustment is made according to a fitting method, which is an adjustment method for providing amplification to a sound pressure level for attaining comfortable hearing.
As necessary, a hearing aid shop further performs a speech sound intelligibility assessment, which involves presenting monosyllabic audios one by one to the user orally or from a CD, and making evaluations as to whether the speech sounds were actually heard, and thus makes a fine adjustment for the hearing aid. Through repetitions of such evaluations and hearing aid adjustments, a hearing aid is obtained which has characteristics suited to the hearing of the user.
However, there has been a problem in that satisfactory adjustments for a hearing aid may not necessarily be made even through such fully-attended adjustments, because such hearing aid evaluations and adjustments are made in a hearing aid shop and by a shop expert.
More specifically, it is in the scenes of daily life that a user of a hearing aid actually wears the hearing aid, e.g., in the household, while watching television, or while going out, and thus the optimum adjustment for the hearing aid will presumably differ from situation to situation. Conventionally, when any dissatisfaction with regard to the adjustment of a hearing aid is felt in the daily life, such scenes of dissatisfaction must be memorized (e.g., conversations are clearly heard but television tends to sound too loud; while there was no problem conversing with an expert at the hearing aid shop, talking to the family still presents a problem in aural comprehension; and so on). Then, such scenes must be conveyed to an expert at the hearing aid shop, based on which the expert makes a readjustment.
The difficulty in such adjustments is that the user needs to recall from memory those past experiences of difficulty of hearing, and try to explain the particular scene(s) and difficulty of hearing to the expert, who tries to estimate out of this dialogue what is appropriate from among a large number of adjustable items with regard to the hearing aid. In the first place, subjective expressions of hearing may permit a lot of variations, and the difficulty of adjustments is further enhanced by reliance on memory.
One solution to such problems may be an approach of making automatic readjustments in scenes of daily life. Known conventional techniques related to this approach are, in particular: a technique of making evaluations based on an objective index (such as an electroencephalogram) rather than making hearing evaluations based on oral reporting (Japanese National Phase PCT Laid-Open Publication No. 2003-533258); a technique of adjusting the reproduced sound based on changes in external ambient sounds (Japanese Patent No. 4145507); a technique of retaining a plurality of fitting parameters and switching between them (Japanese Patent No. 3482465); and so on.
The technique of Japanese National Phase PCT Laid-Open Publication No. 2003-533258 evaluates auditory characteristics for each frequency with respect to pure tones by using an electroencephalogram, based on ASSR (Auditory Steady-State Response). As a result, evaluations can be made without having to provide oral reporting, which would permit large variations from user to user.
The technique of Japanese Patent No. 4145507 ensures that music of the same sound quality is always reproduced irrespective of fluctuations in the external ambient sounds, thus being able to cope with fluctuations in the external ambient sounds to a certain extent.
The technique of Japanese Patent No. 3482465 makes use of a plurality of previously-stored fitting parameters, and switches between the fitting parameters in accordance with the acoustic environment of one's place of living.
The above techniques are techniques of adapting the hearing to the acoustic environment, which differs in each scene of life, and may be useful in making evaluations of hearing without oral reporting.
However, these techniques cannot be used to make evaluations of hearing in the daily life without inconveniencing the user, so as to realize readjustments of a hearing aid in situ. In other words, it is impossible to objectively detect a sound that is difficult for a user to hear in daily life, and make an automatic adjustment. For example, in Patent Document 1, although a user's hearing of a pure tone can be evaluated, evaluations concerning conversational sounds cannot be made. In Japanese Patent No. 4145507, although adjustments in accordance with external sounds can be made to a certain extent, no adjustments are possible that are in accordance with how the user heard them. In Japanese Patent No. 3482465, although a plurality of adjustment parameters may be retained, there is no guarantee that parameters for addressing every possible situation are provided.
For the user, the criterion as to whether or not a hearing aid needs an adjustment should be whether the user himself or herself can easily and aurally comprehend a given sound which is heard through the hearing aid, irrespective of the acoustic environment. In particular, if a phoneme that was difficult to hear can be identified, an adjustment for improving the hearing with respect to that phoneme alone can be made. Generally speaking, each individual adjustment method for hearing aids has a disadvantage in that, while it may be effective for a certain phoneme, other phonemes may be unfavorably affected by it. So long as the conventional adjustment methods are used, adjustments need to be made for every possible sound; however, such adjustments are difficult to make. Therefore, instead of the conventional adjustment methods, it would be effective to employ an adjustment method that addresses phonemes which are difficult to hear while not unfavorably affecting any other phoneme.